Mass production of ophthalmic lenses, in particular hard or soft contact lenses, is usually performed in a fully automated process. One example for such process described in WO 98/42497. In a preferred method of this fully automated mass production the contact lenses are manufactured with reusable molds including male and female mold halves. In one processing station a starting material, e.g. a prepolymer solution, is dispensed into the female mold halves, and the casting molds are then closed with the corresponding male mold halves. Suitable polymers formed by photochemical polymerization and/or cross-linking include polymers based on polyvinyl alcohols (PVA) or silicone hydrogels (SiHy) as well as polymers based on polyethylene glycols (PEG). To perform the photochemical polymerization and/or cross-linking, the starting material contained in the closed molds is exposed to radiation, e.g. ultraviolet radiation. After the polymerization and/or cross-linking step the molds are opened and the contact lenses so formed are removed from the male or female mold halves and transported to further processing stations.
Depending on the materials from which the lens forming surfaces of the molds are made and further depending on the materials the contact lenses are made of, the opening of the molds and the removal of the polymerized and/or cross-linked contact lenses from the male or female mold halves, respectively, may turn out to be a cumbersome task. Adhesive forces between the lens forming surfaces and the formed contact lens may require considerably high forces to allow the opening of the molds and/or to allow detachment and removal of the contact lens from the male or female mold half. Reusable casting molds are known the lens forming surfaces of which are made from highly finished glass, such as, e.g., quartz glass. In combination with specific contact lens materials, e.g. silicone hydrogels (SiHy), the high adhesive forces between the lens forming surfaces and the contact lens may result in an unacceptably high number of contact lenses getting damaged upon opening the molds, and/or upon the subsequent detachment and removal of the contact lenses from the male or female mold halves. Such damages generally render the contact lenses unable to meet the required quality standards.
In EP-0 686 469 and EP-0 740 997 it is suggested to provide an annular flange region extending about a mold surface of a mold half which may be constituted of suitable plastic materials with a thin layer or film of a polymeric surfactant. The thin layer of surfactant is supposed to facilitate removal of excess polymeric material (HEMA) which forms a ring extending externally of the mold cavity. The thin layer of surfactant is applied to the flange regions of the mold halves in a stamping station using a stamping head consisting of a plurality of stamps each of which is adapted to engage respectively a flange region extending about the mold surface. For transferring the polymer surfactant to the stamps a pad arrangement including a reservoir for the surfactant is provided. Alternatively, a brush may be provided which is adapted for contacting the flange region of a mold and which may be connected with a flexible tubing connection leading to a supply source for the surfactant (EP-0 686 469).
The application of the surfactant to the flange region of a mold assists in the separation of the male and female mold halves during opening of the plastic molds, and in addition assists in the removal of the HEMA-rings extending externally of the mold cavity of the molds. These HEMA-rings may otherwise damage the contact lens during demolding due to adhesion to the mold halves of the plastic mold.
However, depending on the lens material used the problem of detaching and removing the contact lens from the male and/or female mold half remains unsolved, particularly in cases where the molded contact lens strongly adheres to the lens forming surfaces of the male and/or female mold halves, as this is the case with contact lenses based on silicon hydrogels. As a result, considerably high forces are still required for the separation of the mold halves, that is to say for opening the mold. In addition, once the mold halves have been separated (the mold has been opened) the contact lenses continue to strongly adhere to the male mold half or to the female mold half, respectively. Moreover, application of the high forces required may result in damages to the ophthalmic lens. It is therefore and object of the present invention to overcome these problems and to provide a method and a device which reduces the considerably high forces required to open the molds and which facilitates detachment and removal of the ophthalmic lenses, e.g. the contact lenses, from the male and female mold halves of the opened lens molds. The solution to these problems shall be capable of being fully integrated in an automated mass production process for molding ophthalmic lenses, in particular soft and hard contact lenses.